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CS378 - Mobile Computing

CS378 - Mobile Computing. Sensing and Sensors. Sensors. "I should have paid more attention in Physics 41" Most devices have built in sensors to measure and monitor motion orientation (aka position) environmental conditions sensors deliver raw data to applications. Sensor Framework.

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CS378 - Mobile Computing

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  1. CS378 - Mobile Computing Sensing and Sensors

  2. Sensors • "I should have paid more attention in Physics 41" • Most devices have built in sensors to measure and monitor • motion • orientation (aka position) • environmental conditions • sensors deliver raw data to applications

  3. Sensor Framework • Determine which sensors are available on a device. • Determine an individual sensor's capabilities, such as its maximum range, manufacturer, power requirements, and resolution. • Acquire raw sensor data and define the minimum rate at which you acquire sensor data. • Register and unregister sensor event listeners that monitor sensor changes. http://developer.android.com/guide/topics/sensors/sensors_overview.html

  4. Sensor Framework • SensorManager • conduit between your classes and Sensors • Sensors • abstract representations of Sensors on device • SensorEventListener • register with SensorManage to listen for events from a Sensor • SensorEvent • data sent to listener

  5. Using sensors

  6. Using Sensors - Basics • Obtain the SensorManager object • create a SensorEventListener for SensorEvents • logic that responds to sensor event • varying amounts of data from sensor depending on type of sensor • Register the sensor listener with a Sensor via the SensorManager • Unregister when done • a good thingto do in the onPause method

  7. Using Sensors • registerListener(SensorEventListener, Sensor, int rate) • rate is just a hint • SENSOR_DELAY_NORMAL, SENSOR_DELAY_UI, SENSOR_DELAY_GAME, or SENSOR_DELAY_FASTEST, or time in microseconds (millionths of a second)

  8. SensorEventListener • Interface with two methods: • void onAccuracyChanged (Sensor sensor, int accuracy) • void onSensorChanged (SensorEvent event) • Sensor values have changed • this is the key method to override • don't hold onto the event • part of pool and the values may be altered soon

  9. Listing Sensors on a Device to Log

  10. Simple Sensor Example • App that shows linear acceleration • options to display current • … or maximum, disregarding direction • Linear Layout • TextViews for x, y, and z • Buttons to switch between max or current and to reset max

  11. Sensor Coordinate System • For most motion sensors: • +x to the right • +y up • +z out of front face • relative to device

  12. Accelerometer - Includes Gravity • Sensor.TYPE_ACCELEROMETER • Device flat on table • g ~= 9.81 m/s2

  13. Sensor Coordinate System • App that displays max acceleration along each axis • Hold phone straight up and down and move to ground

  14. Sensor Coordinate System • Repeat but hold … then sidewaysphone flat

  15. Getting Sensor Data • registerListener • sensorEventListener • Sensor -> obtain via SensorManager • rate of updates, a hint only, or microseconds (not much effect) • returns true if successful

  16. SensorEventListener

  17. Display Max Recall, max range of linear acceleration on dev phone is 19.613 + gravity = 29.423 - a baseball pitcher throwing a fastball reaches 350 m/s2 or more (various "physics of baseball" articles)

  18. Display Current • Lots of jitter • Attempt to zero out???

  19. Types of sensors

  20. Types of Sensors • Three main classes of sensors: • motion (acceleration and rotational forces) • accelerometers, gravity sensors, gyroscopes, and rotational vector sensors • environmental (ambient air temperature and pressure, illumination, and humidity) • barometers, photometers, and thermometers. • position (physical position of a device) • orientation sensors and magnetometers

  21. Types of Sensors • Hardware sensors • built into the device • Software sensors • takes data from a hardware sensors and manipulates it • from our perspective acts like a hardware sensor • aka synthetic or virtual sensors

  22. Types of Sensors - Dev Phone - Older • accelerometer, linear acceleration, magnetic field, orientation, light, proximity, gyroscope, gravity

  23. Sensor Types

  24. Sensor Capabilities - Dev Phones - Older

  25. Types of Sensors - Dev Phone - Newer

  26. Sensor Capabilities - Dev Phone - Newer

  27. Types of Sensors • TYPE_ACCELEROMETER • hardware • acceleration force in m/s2 • x, y, z axis • includes gravity

  28. Types of Sensors • TYPE_AMBIENT_TEMPERATURE • hardware • "room" temperature in degrees Celsius • no such sensor on dev phones • TYPE_GRAVITY • software or hardware • just gravity • if phone at rest same as TYPE_ACCELEROMETER

  29. Types of Sensors • TYPE_GYROSCOPE • hardware • measure device's rate of rotation in radians / second around 3 axis • TYPE_LIGHT • hardware • light level in lx, • lux is SI measure illuminance in luminous flux per unit area

  30. Types of Sensors • TYPE_LINEAR_ACCELERATION • software or hardware • measure acceleration force applied to device in three axes excluding the force of gravity • TYPE_MAGNETC_FIELD • hardware • ambient geomagnetic field in all three axes • uT micro Teslas

  31. Types of Sensors • TYPE_ORIENTATION [deprecated] • software • measure of degrees of rotation a device makes around all three axes • TYPE_PRESSURE • hardware • ambient air pressure in hPa or mbar • force per unit area • 1 Pascal = 1 Newton per square meter • hectoPascals (100 Pascals) • milli bar - 1 mbar = 1hecto Pascal

  32. Types of Sensors • TYPE_PROXIMITY • hardware • proximity of an object in cm relative to the view screen of a device • most just binary (see range, resolution) • typically used to determine if handset is being held to person's ear during a call • TYPE_RELATIVE_HUMIDITY • ambient humidity in percent ( 0 to 100)

  33. Types of Sensors • TYPE_ROTATION_VECTOR (ABSOLUTE) • hardware or software • orientation of device, three elements of the device's rotation vector • TYPE_TEMPERATURE • hardware • temperature of the device in degrees Celsius

  34. Availability of Sensors

  35. Sensor Capabilities • Various methods in Sensor class to get capabilities of Sensor • minDelay (in microseconds) • power consumption in mA (microAmps) • maxRange • resolution

  36. Linear Acceleration • At rest of table • Recall • units are m/s2

  37. Zeroing out • Take average of first multiple (several hundred) events and average • shorter time = more error • Potential error • should be 0 at rest • Results:

  38. Rate of Events • 1000 events • SensorManager.SENSOR_DELAY_UI • times in seconds: 21, 21, 21 • 21 seconds / 1000 events • SensorManager.SENSOR_DELAY_FASTEST • times in seconds: 21, 21, 21 • Recall delay of 20,000 micro seconds • 2x104 x 1x103 = 2x107 = 20 seconds

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